It is known that the exhaust systems for motor vehicles are essentially made up of an exhaust pipe and of a silencer, also called "muffler", which is mainly intended to reduce the exhaust noise down to a legally set limit. To this end, the shapes and dimensions both of the exhaust pipe and the silencer are decisive factors. However, these dimensions and shapes affect negatively and heavily the performance of the engine itself by preventing the free flow of output exhaust gases especially in two-stroke engines, as mostly used in off-road vehicles.
The currently known silencers are made up of a metal housing which delimits the expansion chamber of substantially cylindrical shape and has a diameter greater than that of the exhaust pipe but with limited overall dimensions. These may be of two types: the first one, operating by "resonance or reflection", comprises more chambers fitted in series and in parallel to the outlet pipe of the gases which acoustically filter the more relevant portions of exhaust noise; and the second one, operating by "absorption", comprises a deadening material such as rock wool, placed between the pierced exhaust pipe and the housing, which dissipates the exhaust gases energy into heat by its vibration.
Such currently known silencers share the characteristic of having the housing built from metal in one or more parts fixed to each other and to the exhaust pipe by welds and this causes a string of non-negligible drawbacks; in fact, owing to the high performance required to the engine, the stresses imposed to the exhaust system are heavy and the direct transmission of heat and vibrations to the silencer cause a thermal loss, fast wear and favor the breaking of the housing at the weld points. Whenever a component breaks, it is necessary to replace the whole exhaust system and this implies a relevant expanse. In addition to this, laws which limit the noise produced by the exhaust gases in motor vehicles, especially in off-road vehicles, make these silencer arrangements unsuitable to meet technical as well as economical requirements.